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Invasive alien species are plants, animals, insects, microorganisms, or parasites that are not native to all or parts of the United States which have been introduced from other nations or other parts of the United States, often unintentionally. They are frequently referred to as exotic, non-native, or nonindigenous species. An increasing number of alien species are being found in landscapes across the United States--natural, rural, and urban--and they frequently displace indigenous species, sometimes with very costly results.
In 1992, the number of invasive alien species was estimated by the Office of Technology Assessment to be over 4542 (>2000 plants, 142 terrestrial vertebrates, > 2000 insects and arachnids, 70 fish, 91 non-marine mollusks, and 239 plant pathogens). In the context of sustainable development, an increase in the number of alien species can lead to major disruptions of local and regional ecosystems which continue into the future.
Many of these alien species are introduced through human travel or commerce. Once they become established, these non-native species tend to displace indigenous species, out-competing them for limited food supplies and habitat. Native populations that are fragmented or under stress from natural or human causes are especially vulnerable to the invasion of non-native species. Major outbreaks of disease often occur when pathogens enter new host populations of humans and other species. Newly emerging or re-emerging diseases are of increasing international concern because of the potentially devastating effects they can have on the economy, the environment, and society.
Alien species often spread extremely rapidly due to the lack of natural barriers in their new habitat. Examples include the intrusion of cheat grass in western rangelands; the invasion of zebra mussels in the Great Lakes and the Mississippi River and its tributaries; the appearance of raccoon rabies in the eastern United States; mycoplasmosis in song birds in the United States and Canada; and in the past, fungal chestnut blight and Dutch elm disease which obliterated the American chestnut and elm trees in North America.
References:
• Office of Technology Assessment, U.S. Congress, Harmful Non-indigenous Species in the U.S. 1993 Link(s) to be added, when feasible, to data at level of detail suitable
for use at the community level.
• Friend, M. “Increased Avian Diseases with Habitat Change,” Our Living Resources, National Biological Service, U.S. Department of the Interior, Washington, D.C. 1995.
• National Strategy for Invasive Plant Management, prepared by a national consortium of Federal and non-Federal organizations, 1997.
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http://www.sdi.gov/indicators/lc_alien.htm Last Modified: May 13, 2002 |